Status epilepticus is a condition in which the brain is in a state of persistent seizure. There is evidence that 30-60 minutes of persistent seizure is sufficient to damage neurons and that such a seizure is unlikely to self-terminate. Status epilepticus survivors may die soon after or have severe functional impairments accompanied by neuroinflammation. Longer seizure duration, cerebral insult, and refractory convulsive status epilepticus were strongly associated with poor outcomes suggesting a role for early neuroprotective strategies. See Legriel et al., Critical Care Medicine, 2010, 38 (12):2295-2303. Thus, there is a need to identify improved methods for treating or preventing patients recovering from prolonged seizures.
Cyclooxygenase-2 (COX-2), the inducible isoform of COX, is rapidly upregulated in damaged tissue, for example in the central nervous system (CNS) after a seizure or cerebral ischemia. In the CNS, COX-2 induction overall contributes to neuroinflammation and neurodegeneration by producing prostaglandins. In the periphery COX-2 induction has both beneficial and harmful consequences. Pharmacological inhibition of COX can provide relief from the symptoms of inflammation and pain. Current non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin, ibuprofen, and naproxen, exert their therapeutic effects via nonselectively inhibiting COX. However, multiple downstream COX-2 signaling pathways that promote and oppose tissue injury are complex, which suggests that modulation of a specific prostaglandin receptor could be a superior therapeutic strategy compared with blocking the entire COX-2 cascade.
Prostaglandin E2 (PGE2), a dominant enzymatic product of COX-2 in CNS, can activate four G protein-coupled receptors (GPCRs): EP1, EP2, EP3 and EP4. When activated by PGE2, EP2 stimulates adenylate cyclase (AC) resulting in elevation of cytoplasmic cyclic AMP (cAMP) concentration, which triggers multiple downstream events mediated by protein kinase A (PKA) and exchange protein activated by cAMP (Epac).
In periphery, PGE2/EP2 signaling plays a variety of roles. For example, PGE2 is a major mediator of inflammation and pain. PGE2 is observed as one of the major prostanoid species in inflammatory lesions such as arthritic joints and shows pleiotropic proinflammatory actions in vitro. Direct delivery of PGE2 into tissues can elicit inflammation and ablation of microsomal PGE synthase or EP2 showed reduced arthritic responses in collagen-induced arthritis. Therefore, the beneficial effect of NSAIDs could be at least partially if not fully, caused by their inhibition of PGE2 production, and the PGE2/EP2 signaling pathway might induce inflammation actions observed in chronic inflammatory diseases such as rheumatoid arthritis (RA). In addition, PGE2/EP2 signaling regulates UV-induced acute skin inflammation by increasing skin microenviromental blood flow, and EP2 activation by oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC) might contribute to vascular inflammation. PGE2 signaling through EP2/EP4 exacerbates symptoms of inflammation by increasing IL-23 expression and reducing IL-12/IL-27, which together causes T-cells to differentiate to Th17 effectors both in inflammatory bowel disease (colitis) and arthritis. PGE2/EP2 system up-regulates a variety of inflammatory mediators including chemokines, cytokines, nitric oxide, prostaglandins, etc., to develop and maintain the inflammatory response.
In the brain, based on the phenotype of EP2 knockout mice, it appears that EP2 activation in microglia promotes inflammation and neurotoxicity in animal models of neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Genetic ablation of EP2 receptor reduced oxidative stress and improved cell survival, accompanied by substantial down-regulation of enzymes in glia that produce reactive oxygen species (ROS), such as inducible nitric oxide synthase (iNOS), COX-2, and NAPDH oxidase. EP2 receptor activation by PGE2 upregulates iNOS/NO expression in activated astrocytes by potentiating the response to inflammatory cytokines like TNF-α and IFN-γ.
Because PGE2/EP2 signaling mediates both peripheral and neural inflammation, pharmacological targeting this pathway can have beneficial implications for the treatment of inflammatory diseases. Thus, there is a need to identify agents that can inhibit PGE2/EP2 signaling.
Buchmann et al., (WO/2008/152099) report compositions for the treatment of disorders connected with the EP2 receptor. See also WO2010/012396.